Treatment of sheet materials

ABSTRACT

A PROCESS AND APPARATUS FOR THE UNIFORM PHYSICAL TREATMENT OF A SHEET MATERIAL WITH A GASEOUS FLUID, WHICH UNDER CONVENTIONAL TREATMENT CONDITIONS CAUSES THE SHEET MATERIAL TO UNDERGO UNDESIRED CHEMICAL CHANGES, THE APPARATUS COMPRISES MEANS OD SUPPLY OF SAID GASEOUS FLUID AT A PRESSURE OF AT LEAST TO OR ABOUT ATMOSPHERIC PRESSURE TO DUCING SAID PRESSURE TO OR ABOUT TMOSPHERIC PRESSURE TO SAID SLIT ORIFICE HAVING A WIDTH OF NOT GREATER THAN 8 CM., SAID PRESSURE REDUCING MEANS PROVIDED WITH MEANS TO DISTRIBUTE UNIFORMLY SAID GASEOUS FLUID TO THE SAID SLIT ORIFICE, AND MEANS FOR FORWARDING SAID SHEET MATERIAL AT A CONSTANT RATE ACROSS SAID SLIT ORIFICE.

US. Cl. 8 149.2

United States Patent 01 iice 3,782,899 TREATMENT OF SHEET MATERIALS David Winston Crosby, Pontypool, England, assignor to Imperial Chemical Industries Limited, London, England No Drawing. Filed Aug. 31, 1970, Ser. No. 68,482 Claims priority, application Great Britain, Sept. 2, 1969, 43,328/ 69 Int. Cl. D06c 1/00 4 Claims ABSTRACT OF THE DISCLOSURE A process and apparatus for the uniform physical treatment of a sheet material with a gaseous fluid, which under conventional treatment conditions causes the sheet material to undergo undesired chemical changes, the apparatus comprising means of supply of said gaseous fluid at a pressure of at least 0.35 kg. cm.- gauge, means for reducing said pressure to or about atmospheric pressure to an outlet slit orifice of the said pressure reducing means, said slit orifice having a width of not greater than 8 cm., said pressure reducing means provided with means to distribute uniformly said gaseous fluid to the said slit orifice, and means for forwarding said sheet material at a constant rate across said slit orifice.

The invention relates to apparatus for the physical treatment of a sheet material with a gaseous fluid. More particularly it relates to apparatus for the physical treatment of a porous or permeable sheet material with a gaseous fluid under conditions at which the'fluid is liable to chemically attack the sheet material and to cause an undesired chemical change in the sheet material.

The treatment of sheet materials, such as textile materials or polymeric films, with a gaseous fluid in order to eifect some physical change in the properties of the sheet material is Well known. Examples of such treatments include the setting operations performed on textiles using hot air or steam, decatising of woolen textile materials, the bonding of non-woven materials containing thermoplastic fibers by hot air or steam, the bonding of non-woven materials containing fibers which may be plasticized by suitable solvent vapors and the leaching of a plastics sheet to introduce fibrillateability thereto. However, it frequently happens that a gaseous fluid which is eminently suitable by virtue of certain of its properties, such as heat conductivity, cheapness and non-toxicity, is found to chemically react with the sheet material and to cause undesired chemical changes therein. A typical example is the use of hot air to bend a non-woven material containing polyamide fibers: at the bonding temperature the polyamide molecules undergo chemical modification, a phenomenon referred to as degradation.

In order to adequately treat the sheet materials a large quantity of treatment fluid is necessary and therefore prior art devices have employed means for recirculation of the fluid. Consequently such prior art devices have comprised a fluid supply, recirculation fan, treatment conveyor and in the case of a hot treatment fluid, a reheater all enclosed within a chest, and are as a consequence bulky, cumbersome and expensive.

To minimize degradation the residence time in the treatment zone must be short. Consequently, either the sheet material must be passed rapidly through the treatment 3,782,899 Patented Jan. I, 1974 zone, or the apparatus must be designed so that the treatment zone is short in the direction of travel of the sheet material. However, long narrow recirculating devices having a short treatment zone in the direction of travel of the sheet material have been found to give extremely poor distribution of the treatment fluid across the width of the sheet material and are as a consequence impractical. Consequently it has been the practice in the past to pass the sheet material rapidly through the treatment zone in order to reduce degradation to a tolerable level. Such a consideration has usually necessitated a batch-wise operation, since the rate of production of, for example, textile materials has been much slow to contemplate a continuous physical treatment in the production line without the textile material suffering corresponding chemical degradation. Typical processing speeds on conventional apparatus have been of the order of 15-25 cm./sec. in order to minimize degradation.

In certain processes, it would be desirable to be able to employ a continuous process of physical treatment of a sheet material with a gaseous fluid without chemical degradation of the sheet material and. it is therefore an object of the present invention to provide suitable apparatus for so doing. Accordingly the invention provides, in one of its aspects apparatus for the uniform physical treatment of a sheet material with a gaseous fluid which, under conventional treatment conditions, causes the sheet material to undergo undesired chemical changes, said aparatus comprising a means of supply of said gaseous fluid under a pressure of at least 0.35 kg. cm. gauge, preferably at least 1.00 kg. cm." gauge, means for reducing said pressure to or about atmospheric pressure, said pressure-reducing means provided with means to distribute uniformly said gaseous fluid to an outlet slit orifice of the said pressure reducing means, said slit orifice having a width of not greater than 8 cm., and means for forwarding said sheet material at a constant rate across the said slit orifice.

The treatment fluid should be supplied at a pressure of at least 0.35 kg. cm. since we have found that, with lower pressures, uniform distribution of the treatment fluid along the length of the slit orifice cannot be achieved. The slit orifice should have a width not greater than 8 cm. since otherwise the rate of consumption of treatment fluid, which is not recirculated, becomes excessive, and the apparatus becomes uneconomical. Direct recirculation of the treatment fluid is not possible since firstly it becomes diluted with atmospheric gases and secondly it would have to be compressed, which would make recirculation more expensive than allowing the treatment fluid to escape to the atmosphere.

In another of its aspects the invention provides a process for the treatment of a sheet material with a gaseous fluid which, under conventional processing conditions, causes undesired chemical change in said sheet material, comprising passing said sheet material through a zone in which said gaseous treatment fluid is at a con centration of at least 99% and flowing at a rate of at least 60 cm. secpreferably cm. seeeach point in said sheet material being within said zone for a period of not more than 5 seconds preferably not more than 1 second and being exposed to substantially the same quantity of treatment fluid as all other points.

The zone in which the treatment fluid is concentrated will be not less in area than the area of the slit orifice.

The slit orifice may for example pass the treatment fluid into an enclosed chest through which the sheet material is arranged to pass: in this case the treatment zone will occupy the entire chest.

Modern techniques of producing non-woven fibrous sheet materials have made it possible to produce such materials at rates of, say, 7 cm./sec. The apparatus of the invention has been found to be eminently suitable for the continuous treatment of such materials.

The pressure reducing means of the apparatus which is provided with means to distribute the gaseous fluid uniformly to the slit orifice conveniently comprises a hollow chest provided internally with bafile means. The bafiles may conveniently be a series of bafile plates. Additional baffles and distributors may be provided immediately behind said slit orifice, and are conveniently formed as screens of foamed metal or of porous sintered metal. When the treatment fluid is at a temperature above the ambient temperature the pressure reducing means may with advantage be insulated and if necessary external heating of the pressure reducing means may be supplied. Additionally the sheet material may, if desired, be pre-heated to some temperature at which the sheet material remains unchanged and subsequently passed through the treatment zone. Pre-heating may be carried out by means of heaters which may be independently heated, or by means of the hot treatment fluid. Pre-heating of the sheet structure may additionally serve to minimize vapor condensation on the sheet structure.

The sheet material may be carried across the slit orifice from which the treatment fiuid issues by transporting means such as permeable conveyor belts or if the nature of the sheet material permits, it may be passed across the slit orifice without additional support. In one embodiment of the invention, a conveying means is provided with a pattern of permeable and impermeable components and interposed between slit orifice and sheet material so that the sheet material is treated only in certain areas corresponding to the permeable regions of the conveying means. Alternatively, the sheet material may be interposed between two permeable conveyor belts which support it While it is being treated, and this is particularly useful when it is of a very delicate nature, such as a low-weight unbonded non-woven web.

The treatment fluid issuing from the slit orifice of the apparatus may pass through the sheet structure without further assistance, or alternatively, suction may be applied by means of a slot to the side of the sheet structure remote from the slit orifice. The suction slot serves to drag the treatment fluid through the sheet structure and this arrangement is particularly valuable when a sub stantially uniform treatment throughout the thickness of a thick structure is required.

Preferably the slit orifice is at least as long as the sheet material is wide, in which case the sheet material can be passed over the slit orifice in a direction at least substantially perpendicular to the axis of the slit. The apparatus however may be used to treat a slit material having a width greater than the length of the slit orifice. In the latter case it is necessary to cause a relative reciprocal traversal motion between slit orifice and sheet material. Usually the slit orifice of the apparatus will be traversed reciprocally across the sheet material and it is convenient to cause the axis of the slit orifice to be parallel to the edges of the sheet material. In order to ensure uniform treatment of the sheet material the speed of traverse and speed of advance of sheet material should be chosen so that ratio of the length of the slit orifice to the length which the sheet material advances during one complete traverse cycle of the treatment apparatus in an integer.

Optionally, the sheet material may, after the desired physical treatment, be exposed to a second fluid treatment which serves to restore the sheet structure to the ambient conditions pertaining before the first treatment. This second treatment is referred to, for convenience, as a quenching treatment. For example, where the treatment fluid comprises a hot vapor, the quenching treatment may comprise a blast of cool vapor. Such treatment has been found to be particularly useful in the treatment of thermoplastic structures, especially at high temperatures, since the risk of degradation is further reduced.

Although the main embodiment of the invention provides a means of uniformly treating the sheet material across its width it is possible to vary the amount of treatment throughout the thickness of the sheet material. Thus, by employing a single treatment slit orifice, at low rates of flow of treatment fluid, the degree of treatment through the sheet material may vary from intense treatment at the surface in contact with the slit to very little treatment at the surface remote from the slot. Similarly, by using two slits, one on each side of the sheet structure, intense treatment at the surfaces with less treatment at the middle of the sheet structure is obtained, and as intimated above, a suction slot in combinaion with the slit orifice can be used to obtain uniform treatment throughout the thickness of a thick structure.

The apparatus of the invention finds particular use in the treatment of textiles of synthetic filaments or fibers. We have found that its performance in the in-line bonding of the synthetic organic polymeric filaments constituting a non-woven fabric is particularly valuable. With this apparatus it has become possible to bond in the production line non-woven fabrics comprising polyamide fibers (which may be multi-component) using either superheated steam or hot air as the treatment fluid without suffering unacceptable degradation of the polymeric fibers.

The following examples which are not intended to limit the scope of the claims appended hereto in any way, compares the properties of non-woven fabrics, bonded by steam or air, on conventional equipment and apparatus according to the invention.

EXAMPLE 1 In this example portions of non-woven web composed of polyamide filaments are bonded by treatment with hot air and the appearance and physical properties are assessed.

The non-woven web was composed of con tinuous bicomponent filaments of count 3-4 denier, the bicomponent filaments possessing a core-sheath arrangement, the core being of nylon 6.6 and accounting for 65% of the weight of the filament, and the sheath, completely and substantially concentrically surrounding the core being (23f nylon 6. The Weight of the web was about 103 g. m.--

A first portion of the web was bonded by exposure to hot air in a conventional recirculating oven. The oven, consisted of a conveyor arranged to receive the unbonded web and to transport it through the treatment zone. A recirculating pump sucked hot air through the web and passed the air to a heater and after which it was ducted back to above the web. The hot air in the vicinity of the Web was about 60 cm. S6C. 1.

A second portion of the same web wa bonded, also by exposure to hot air by passage through apparatus according to the invention. Hot air was supplied at a pressure of about 3.5 kg. cm.- gauge to a pressure reducing means having internal dimensions of 4.45 cm. x 4.78 cm. x 38.2 cm. and was distributed uniformly along the length of the apparatus by means of bafiles.

The baffies were made of 0.15 cm. thick aluminum sheet and occupied the entire internal cross-section of the pressure reducing means, parallel to the base thereof. Holes were provided within the bafllles, the number and size thereof being different in each bafiie. Hot air was supplied at a point midway along the top surface: the first baflie was provided with two holes of diameter 0.64 cm. spaced at half the distance between center of bafiie and walls of the apparatus. The bafiles were equispaced. Details of the arrangements of holes in the baffles is given in the following table: Battle 1 is topmost, Bafile 5 is just behind the slit orifice.

Size of No. of holes,

Baffle holes Position of holes cm.

1 2 1 central row, each hole 9.5 cm. from edge 0. 64

2 4 1 central row, holes equispaced by 9.5 cm., and 0. 32

holes in baflie 1 being centrally positioned between two holes.

3 8 1 central row, holes equispaced by 4.75 cm., 0.22

each hole in battle 2 being centrally positioned between two holes.

4- 16 1 central row, holes equispaced by 2.4 cm., each 0. 15

hole in bafile 3 being centrally positioned between two holes.

5- 64 2 rows of 32 holes, each row positioned 9g of dis- 0. 64

tance across baflie, holes equispaced by 1.2 cm., each hole in bafiie 4 being equidistant from 4 holes, two in each row.

Thereafter the hot air flowed through a slit orifice measuring 1.27 cm. in width. A stationary perforated metal screen, curved concavely to the slit orifice, having a radius of curvature in the plane of the widthwise direction of the slit orifice of about 40 cm. was provided over which the web, sandwiched between two woven fabric conveyor belts, was passed. Hot air issued from the slit orifice at a rate of approximately 600 cm. secf In both trials the hot air temperature was 220 C. and the web was passed through the bonding apparatus at l m. minr The quality of the bonded web was assessed by measurement of its breaking load and extensibility to yield, and the degree of degradation was assessed by observing the color of the Web, measurement of the relative viscosity of the polymer, and also by measuring the value of B- chromaticity (a scale of color: higher figures indicate white fabric). The results are tabulated below: by way of comparison the properties of the unbonded Web is in cluded where applicable.

Web bonded in- Apparatus Unbonded Prior art of the Property web apparatus invention Breaking load, kg 1. 53 4 41 Extensibility, percent 18. 2 30. 5 Appearance to eye White Brown Color-B-chromaticity 0. 332 0. 213 0. 303 Relative viscosity of polymer 44. 2 11. 5 24. 6

1 Undetecteble difierence in color to unbonded web by naked eye.

The results clearly show that while the web is bonded in both types of apparatus, at the low processing speed chosen, the prior art oven causes unacceptable discoloration and loss of breaking load and extensibility. The severe degradation of the polymer is shown by the extremely low value of relative viscosity. On the other hand, the degradation occurring in the apparatus of the invention is much less and is shown in the relative viscosity.

EXAMPLE 2 steam. Apart from the change in treatment fluid, all other conditions, material, and tests were unchanged from Example 1.

The properties of the bonded webs are given in the following table:

1 Undetectable change in color.

In this case both apparatus produced bonded webs having properties greatly superior to those of the previous example. However, the web bonded by the apparatus of the invention was considered to have superior physical properties and was shown to be less degraded.

The examples show, most interestingly, that the apparatus can possible satisfactorily bonded webs with hot air as the treatment fluid. This may be desirable in cer tain cases when it is desired to avoid the exhaust of steam into the atmosphere: for example, in a humidity controlled area in which polyamide filaments are being meltspun.

What I claim is:

1. A process for the uniform physical treatment of a porous sheet material with a gaseous fluid while avoiding undesired chemical changes within the sheet material comprising supplying the gaseous. fluid at a pressure of at least 0.35 kilograms per square centimeter, reducing the pressure to about atmospheric pressure and flowing the fluid through a narrow slit to form a treatment zone in which the fluid is distributed uniformly along the length of the slit and in which the fluid flows at a rate of at least 60 centimeters per second, and forwarding the sheet material through said zone in a direction across the slit at a constant rate of a magnitude such. that each point in said sheet material is in the zone for a period not greater than 5 seconds whereby each point is exposed to sub stantially the same quantity of fluid as all other points.

2. A process as in claim 1 including imparting reciprocal movement between the sheet material and the slit such that the slit traverses the width of the sheet material during forwarding of the latter.

3. A process as in claim 1 wherein the web is a porous non-woven web containing polyamide filaments and wherein the fluid is a heated fluid which bonds the filaments during the treatment.

4. A process as in claim 3 wherein the non-woven web is forwarded through the treatment zone at a rate not greater than about 8 centimeters per second.

References Cited UNITED STATES PATENTS 1,251,173 12/1917 Beregh 34--160 3,238,635 3/1966 Gravenstreter 34-160 X 3,457,029 7/1969 Drago 8-149.3

WILLIAM I. PRICE, Primary Examiner U.S. Cl. X.R. 8-1493 

